Lore is not a diminutive, but rather, it is a (contracted) short form of Eleonore. If it were a diminutive, then a German diminutive suffix would have been part of the name, such as -chen (Lorechen, Lorchen) and -lein (Lorelein). See also:

With that said, Lore is also in use in Belgium (particularly in the Flanders region) and the Netherlands, where it is also a short form of Eleonora and Eleonore. The name is currently common in Belgium, but it is rare in the Netherlands. It is (very) slowly gaining in popularity there though, as it fits perfectly in the current Dutch naming trend of ultra-short names.